24 July 2021 Structural Steel Bar
18CrMo4 Structural Steel Bar
18CrMo4 (1.7243 ) is a kind of steel with high permanent strength at 500～550℃. When the temperature exceeds 550℃, the oxidation resistance becomes worse and the creep strength is significantly reduced. 18CrMo4 belongs to the European standard alloy carburized steel, belongs to standard: EN 10084-2008. 18CrMo4 (1.7243) alloy structural steel has good process performance and welding performance, and has a higher endurance strength at 500-550°C.
When the temperature exceeds 550°C, the oxidation resistance will deteriorate and the creep strength will decrease significantly. If under 500-550 ℃ for a long time, the thermal strength of 18CrMo4 steel will decrease, and the strength will decrease. 18CrMo4 is used to make 510℃ high and medium pressure steam pipes, headers, superheaters and forgings whose tube wall temperature is 550℃.
Chemical Composition:
| C(％) | Si(％) | Mn(％) | P(％) | S(％) | Cr(％) | Ni(％) | Cu(％) | Mo(％) |
|---|---|---|---|---|---|---|---|---|
| 0.15～0.21 | ≤0.40 | 0.60 ~ 0.90 | ≤0.035 | ≤0.035 | 0.90～1.20 | ≤0.030 | ≤0.030 | 0.15 ~ 0.25 |
Mechanical properties - 18CrMo4:
| Mechanical and physical properties | ||
|---|---|---|
| Tensile strength | Rm | > 1080 MPa |
| Yield point | Re | > 880 MPa |
| Contraction | Z | > 50% |
| Elongation | A | > 10% |
| Notch toughness | KU2 | > 72 J |
| Hardness in softened state | HB | < 217 HB |
| Density | ρ | 7,85 kg/dm3 |
Mechanical properties for individual dimensions:
| Mechanical properties after hardening | ||||
|---|---|---|---|---|
| Properties | Dimensions | |||
| 11mm | 30mm | 63mm | ||
| Tensile strength | Rm | 920 - 1270 MPa | 820 - 1170 MPa | 710 - 1060 MPa |
| Yield point | Re | > 600 MPa | > 540 MPa | > 480 MPa |
| Notch toughness | KU | > 25 J | > 25 J | > 25 J |
| Elongation | A | > 9 % | > 10 % | > 11 % |
Heat treatment of 18CrMo4 steel:
| Process | Cooling | Temperatures |
|---|---|---|
| Normalizing annealing | in air | 870 - 900℃ |
Softening annealing | 650 - 700℃ | |
| Carburizing in powder |
| 880 - 950℃ |
| Carburization in salt baths | 900 - 950℃ | |
| Gas carburization | 880 - 900℃ | |
| Hardening (I) |
| 860 - 900℃ |
| Hardening (II) |
| 800 - 840℃ |
Tempering | 170 - 200℃ | |